Vision tests. Your doctor may ask you to read letters on a chart to test your vision in a visual acuity test.

Test to measure the curvature of your cornea. By measuring light reflected from the surface of your cornea, a device called a keratometer measures the amount of curvature to your cornea's surface and can confirm the presence of astigmatism. This test is called keratometry.

The curvature of your cornea is an important piece of information for contact lens fitting. The curvature tends to be irregular in astigmatism.

To measure variations in corneal surface curvature, doctors may use a process called computerized corneal mapping. Computerized corneal mapping uses a keratoscope fitted with a video camera (videokeratoscope) to create a map of your cornea's surface.

Test to measure light focus. To measure how your eyes focus light, your eye doctor may place different lenses in front of your eyes using a device called a phoropter.

Your doctor may also use a device called a retinoscope, which directs a beam of light into your eye, to determine how your eye focuses light.

These procedures can assess the degree of your refractive error and help calculate prescriptions for contact lenses and glasses.

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